Bacterium
Ehrlichia chaffeensis
Obligate intracellular tick-borne bacterium of monocytes
err-LIK-ee-uh chuh-FEEN-sis
High-yield clue
Mulberry-shaped clusters (morulae) inside monocytes on a blood smear are the classic study clue.
Overview
An obligate intracellular Gram-negative bacterium in the order Rickettsiales that replicates inside monocytes and is the agent of human monocytic ehrlichiosis (HME). It is a high-yield example of a tick-borne intracellular pathogen studied alongside Anaplasma and Rickettsia.
Classification
- Gram-negative
- Obligate intracellular
- Order Rickettsiales
- Family Anaplasmataceae
Lab & identification clues
- Morulae in monocyte cytoplasm vocabulary
- PCR/NAAT detection concept
- Serology (IFA) concept
- Poorly seen on routine Gram stain
Associations
- Lone star tick (Amblyomma americanum) transmission
- White-tailed deer reservoir vocabulary
- Southeastern/south-central US epidemiology
- Fever-headache-myalgia study presentation
Commonly confused with
- Anaplasma phagocytophilum
- Rickettsia rickettsii
Frequently asked questions
What is Ehrlichia chaffeensis?
An obligate intracellular Gram-negative bacterium in the order Rickettsiales that replicates inside monocytes and is the agent of human monocytic ehrlichiosis (HME). It is a high-yield example of a tick-borne intracellular pathogen studied alongside Anaplasma and Rickettsia.
What is the Gram stain of Ehrlichia chaffeensis?
Ehrlichia chaffeensis is Gram negative.
What are the lab clues for Ehrlichia chaffeensis?
Lab clues for Ehrlichia chaffeensis include Morulae in monocyte cytoplasm vocabulary, PCR/NAAT detection concept, Serology (IFA) concept, and Poorly seen on routine Gram stain.
What is Ehrlichia chaffeensis commonly confused with?
Ehrlichia chaffeensis is commonly confused with Anaplasma phagocytophilum and Rickettsia rickettsii.
Original student-study summary. Sources checked: OpenStax Microbiology 2e, NCBI Bookshelf Medical Microbiology, and CDC topic pages where applicable; reviewed 2026-06. Educational only; no diagnosis, treatment, dosing, or specimen-handling guidance.